Conditional divorce is effective.

The Shaykh : If a man says to his wife, "If you do such-and-such, you are divorced," and she does it, what happens? She is divorced. This is the view held by the majority of scholars, including the four schools of jurisprudence. All four schools agree that if a man says to his wife, "You are divorced if you do such-and-such," and she does it, she is divorced. They do not consider this an oath; they do not consider it an oath. Therefore, the matter is very serious, and one must be careful not to be lax in this issue. Allah the Exalted says: